The invention relates generally to apparatus for carrying out a process that uses supercritical fluids, such as, for example, a process for preparing coating materials as described in U.S. Pat. No. 5,399,597 and co-pending U.S. patent application Ser. No. 08/438,681 entitled "CONTROL SYSTEM FOR PROCESSES USING SUPERCRITICAL FLUID", the entire disclosures of which are both fully incorporated herein by reference. More specifically, the invention relates to improvements and alternative embodiments of the mixing system including the pressure vessel and agitator that are part of the overall system described in the aforementioned disclosures.
The systems described in the referenced disclosures are effective for many processes that use supercritical fluids. However, improvements in the delivery and recovery systems for the process media have been discovered which can significantly improve the overall performance and quality of the finished product for different reaction processes.
The systems described in the above-identified references include pumps for delivering the process media to the reactor vessel (also referred to herein as the pressure vessel) in a supercritical state. The delivery system includes a surge accumulator to dampen pressure surges from pump activation, and also includes a heat exchanger to control the media temperature while the media is pumped to the pressure vessel. It has been empirically observed that control of the flow of the process media to the pressure vessel is an important aspect of the overall system performance. Delivery of the media is important during both the reaction process within the pressure vessel as well as during delivery of the finished reaction mixture from the pressure vessel to the receiver vessel. The delivery process in particular places significant demands on the control system in order to assure isobaric delivery of the finished reaction to the receiver vessel. In order to meet the substantial demand for mass flow of the process media, large pumps are typically required. However, in some applications, particularly pilot plants for example, the use of large pumps may not be a suitable solution due to noise, power requirements, space and so forth.
Recovery of the process media is also an important aspect of the overall system described in the referenced disclosures. Recovery of the process media includes the need to determine the condition of the media after the reaction process. For example, knowledge of whether material has dissolved in the process media can be important for determining what level of distillation is required in order to recover the process media in a condition that it can be used for another reaction process without contaminating the new process.
The objectives exist, therefore, to provide a process media delivery and recovery system that improves the flexibility and utility of supercritical process systems as such as are described in the aforementioned disclosures.